1. Field
One embodiment of the present invention relates to a method of manufacturing a stamper used for mass production of magnetic recording media by transferring patterns by an imprint technique.
2. Description of the Related Art
In recent years, there has been known a problem that improvement in track density is hindered by interference between adjacent tracks in a magnetic recording medium to be installed in a hard disk drive (HDD). In particular, it is an important technological problem to reduce fringing of a write head field.
To address the problem, a discrete track recording medium (DTR medium) has been developed in which recording tracks are physically separated from each other. The DTR medium can reduce the side erase phenomenon that the information of an adjacent track is erased in a write operation and the side read phenomenon that the information of an adjacent track is read out in a read operation, leading to an improved track density. Therefore, the DTR medium is expected as a high-density magnetic recording medium.
For producing the DTR medium, a nano-imprint method using a nickel (Ni) stamper is employed as disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2008-12705. First, a resist layer is formed on a substrate such as glass or Si, subjected to electron-beam (EB) lithography and developed to manufacture a master plate having patterns of lands and grooves. A Ni conductive layer is formed on the surface of the master plate and a Ni electroforming layer is formed on the Ni conductive layer, and the Ni conductive layer and Ni electroforming layer are peeled off to manufacture a father stamper. A mother stamper is likewise manufactured from the father stamper using a method in which a Ni conductive layer and a Ni electroforming layer are formed and then peeled off, and further, a son stamper is likewise formed from the mother stamper. Next, a magnetic recording layer is formed on a medium substrate and a resist is applied to the magnetic recording layer. The resist is imprinted with the son stamper to transfer patterns of lands and grooves of the son stamper to the resist. The magnetic recording layer is etched using the resist pattern as a mask to form a DTR medium.
In order to achieve high-density recording, it is required to form the patterns of lands and grooves at a track pitch of 100 nm or less. If it is intended to form the patterns of lands and grooves on the master plate at a high density, the time for electron beam lithography is prolonged. At this time, the electron beam writing performance is more improved with decrease in the thickness of the resist. Therefore, there is a tendency that the thickness of the resist is made smaller with increase in the density of the patterns of lands and grooves. As a result, the land height on the surface of the master plate is decreased and, accordingly, the land height on the surface of the stamper is decreased. However, if a stamper with a land low in height is used, the patters of lands and grooves transferred to the resist on the medium may have defects because of insufficient transfer during imprinting. Also, even if the track pitch is made small, it is necessary for the lands to have a width enough to maintain performance to read from and write to the track, i.e., the land. For this purpose, it is necessary to form grooves having a small width by EB lithography in the production of the master plate. It is however difficult to write grooves having a width of several nanometers because of the limitation of an EB writing apparatus. Therefore, current technologies have such a problem that a high-density master plate is not provided.